In recent years, national expenditures or prescription drugs have increased rapidly. Consistent with this trend, managed care organization (MCOs) have experienced pharmaceutical Cost growth of 10 to 17 percent annually. To stem this growth, MCOs have adopted various strategies, including three-tier prescription drug copayment programs (TPPs). This strategy varies the drug cost share paid by consumers, depending upon whether the prescription is for a generic (tier 1), preferred brand (tier 2) or non-preferred brand (Tier 3). Despite the recent widespread adoption of TPPs by MCOs, Ivery little is known about the effect of these programs on drug and other medical services use and cost containment. Further, there is some concern that patients' therapeutic continuity of care may be adversely affected. Using segmented time series and two-part regression analytic techniques, this two-year study will examine the impact of a TPP on drug and medical services utilization, expenditures and therapeutic continuity of care. The analyses will use continuously enrolled patient cohorts in the Tufts Health Plan (THP), a large health maintenance organization in Massachusetts. Enrollment, drug claims and medical claims data will be extracted and made into analytic files by Tufts Health Plan. Specifically, this study will address three study aims: 1. What is the impact of the TPP on prescription drug use and spending? 2. What is the impact of the TPP on other medical services use and spending? 3. What is the impact of the TPP on patients' therapeutic continuity of care? Findings from this study will be useful to policymakers, health care providers, clinicians and others interested in the effects associated with drug cost-containment initiatives.